The present invention relates to a fiber optical coupler for coupling energy lights from a plurality of systems into a single optical fiber (light guide fiber). For example, the invention relates to an optical fiber coupler for coupling laser beam transmitted by a plurality of optical fibers, in particular the one for coupling power laser beams transmitted by a plurality of optical fibers.
The energy lights transmittable through optical fiber includes illuminating lights, laser beams, etc. When these illuminating lights and laser lights were transmitted through the optical fiber, one light source device or one laser oscillator was optically connected to a single optical fiber. Then, through this single optical fiber the energy lights were transmitted to their utilization points. When a power exceeding the maximum output of one laser oscillator is necessary, outputs from a plurality of laser oscillators must be combined and a workpiece must be irradiated with them. Similarly, in the case where illuminating light transmission by this type of optical fiber is applied to an illuminating light transmitting device needing a large light quantity, it is also necessary to couple illuminating lights from a plural number of optical fibers respectively connected to a plurality of illuminators with a single optical fiber. Further, when power laser beams and guiding visible laser beams are transmitted by one and the same optical fiber, it is necessary to couple power laser beams from the optical fiber therefor and visible laser beams from the optical fiber therefor.
Thus, conventionally, various types of fiber optical coupling systems have been offered. For example, according to the one disclosed in Japanese Patent No. 2-50105, as shown in FIG. 10, power laser beams emitted from the optical fibers 100 are made to parallel lights respectively by the very small collimating lenses 101. These paralleled power laser beams are made incident on different parts of the single condenser lens 102. Then, the optical axes of these power laser beams are bent toward the focus of the condenser lens 102 and converged thereat. At this coupling system in FIG. 10, a workpiece was directly disposed on the focus of this condenser lens 102 and processed.
According to the one disclosed in Japanese Patent 4-322892, as shown in FIG. 11, after power laser beams of plural systems are made to parallel beams respectively, they are disposed in parallel to one another using prism type mirrors 200. These parallely disposed power laser beams are made incident on a plurality of places of the single condenser lens 201 including the central axis. Then, they are converged by the condenser lens 201 and made incident on the optical fiber at the downstream side. However, at the fiber optical coupling systems of these conventional types, various problems as described below were created.
At the one disclosed in Japanese Patent No. 2-50105, when a workpiece is disposed on the focal surface 104, though focuses can surely be coupled on a single spot, laser beams can not be coupled on the front and rear thereof. That is, the spot is divided into three different ones. Thus, even if it is considered that the optical fiber on the downstream side is disposed on the rear side of the condenser lens 102 and laser beams are coupled, it will be difficult to put it into practice, as it is made necessary to exactly dispose the incident plane of the optical fiber on the downstream side on the focal surface 104. In particular, when the one having a small diameter is used as the optical fiber on the downstream side, it will be almost impossible to realize it, as it is made necessary to adjust the position of a high precision optical device.
Further, at the one disclosed in Japanese Patent No. 4-322892, the optical axes of irradiated power laser beams must be disposed in a direction orthogonal to the optical axis of the condenser lens 201 and the reflection surfaces of the prism type mirrors 200 must be disposed inclined 45.degree. respectively against the optical axes thereof. Likewise, respective optical elements must be precisely arranged. When a single condenser lens is used, it may not be easy to prevent the effect of aberration(astigmatism). Therefore, power laser beams made incident on the vicinity of the optical axis of the condenser lens 201 are converged into focus afar while those made incident on the peripheral part thereof are converged into focus near and they are never converged at one place. Further, beam forms are distorted by reflection of the prism type mirrors, and as the effects of heated lens phenomena by the condenser lens 201 are made ununiform when differences in outputs of the respective power laser beams are generated, the beam forms will be further distorted and shifts will be generated in the focuses. Thus, in particular, when the one having a small diameter is used as the optical fiber on the downstream side, it will be difficult to make all the power laser beams incident on this optical fiber and couple them.
As described above, at any of the conventional fiber optical coupling systems, it was difficult to make the energy beams from plural systems incident on the optical fiber with a small diameter and couple them. Further, even if it is possible to couple them on the incident plane of the optical fiber on the downstream side at certain output values by precisely arranging the optical elements, shifts in the optical axes and multifocuses at condensing points will be generated by the heated lens fluctuations of the optical elements when the output values are changed. Thus, parts other than the core of the fiber is irradiated with high power beams causing damages to the edge surface and internal parts.